Lithographic apparatus and device manufacturing method

ABSTRACT

A gas knife configured to dry a surface in an immersion lithographic apparatus is optimized to remove liquid by ensuring that a pressure gradient is built up in the liquid film on the surface being dried.

This application is a continuation of U.S. patent application Ser. No.14/792,143, filed Jul. 6, 2015, now allowed, which is a continuation ofU.S. patent application Ser. No. 12/901,939, filed Oct. 11, 2010, nowU.S. Pat. No. 9,099,501, which is a continuation of U.S. patentapplication Ser. No. 11/167,552, filed Jun. 28, 2005, now U.S. Pat. No.7,834,974, each of the foregoing applications is incorporated herein inits entirety by reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent application WO99/49504, hereby incorporated in its entirety by reference. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletIN onto the substrate, preferably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet OUT after having passed under the projection system. That is, asthe substrate is scanned beneath the element in a −X direction, liquidis supplied at the +X side of the element and taken up at the −X side.FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet IN and is taken up on the other side of the element by outletOUT which is connected to a low pressure source. In the illustration ofFIG. 2 the liquid is supplied along the direction of movement of thesubstrate relative to the final element, though this does not need to bethe case. Various orientations and numbers of in- and out-letspositioned around the final element are possible, one example isillustrated in FIG. 3 in which four sets of an inlet with an outlet oneither side are provided in a regular pattern around the final element.

There are many circumstances in immersion lithography in which one ormore surfaces are covered in immersion liquid. Many of these surfacesmust then be cleared of immersion liquid further down the manufacturingprocess.

SUMMARY

Accordingly, it is desirable to provide an immersion apparatus with aneffective means to remove immersion liquid from a surface.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate through a liquid, the apparatuscomprising a gas knife configured to provide gas onto a surface, anextractor adjacent the gas knife to remove gas, liquid, or both, and aflow regulator configured to control a gas flow rate out of the gasknife to be within 20% of a gas flow rate into the extractor.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate through a liquid, the apparatuscomprising a gas knife configured to provide gas to a surface, whereinthe gas knife comprises an outlet to exit gas, the outlet having a widthof between 10 and 50 μm and a length of between 100 and 500 μm.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate through a liquid, the apparatuscomprising a gas knife configured to provide gas to a surface to bedried at an angle to the surface of between 70° and 85°.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate through a liquid, the apparatuscomprising a gas knife configured to provide gas to a surface to bedried, a first extractor, and a second extractor, the first and secondextractors being on opposite sides of the gas knife and configured toremove gas, liquid, or both, from the surface.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate through a liquid, the apparatuscomprising a gas knife configured to remove a liquid from a surface, thegas knife arranged such that passage of the liquid is blocked by aformation of a pressure gradient in the liquid.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting through an immersion liquid apatterned beam of radiation onto a substrate, wherein immersion liquidis removed from a surface by a flow of gas from a gas knife to anextractor positioned adjacent the gas knife, the gas flow rate out ofthe gas knife being within 20% of the gas flow rate into the extractor.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting through a liquid a patternedbeam of radiation onto a substrate, wherein liquid is removed from asurface by a flow of gas out of an outlet of a gas knife which outlethas a width of between 10 and 50 μm and a length of between 100 and 500μm.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting through a liquid a patternedbeam of radiation onto a substrate, wherein liquid is removed from asurface by a flow of gas impinging on the surface at an angle of between70° and 85°.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting through a liquid a patternedbeam of radiation onto a substrate, wherein liquid is removed from asurface by formation of a pressure gradient in the liquid by gas.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting through a liquid a patternedbeam of radiation onto a substrate, wherein passage of liquid is blockedby formation of a pressure gradient in the liquid by gas.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, another liquid supply system for usein a lithographic projection apparatus;

FIGS. 6 and 7 illustrate half of a liquid supply system, incross-section, in which a gas knife is used; and

FIG. 8 illustrates, in schematic cross-section, a gas knife according toan embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or DUV radiation).

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam B. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam B, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-) magnification and image reversalcharacteristics of the projection system PS. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another solution which has been proposed is to provide the liquid supplysystem with a liquid confinement structure which extends along at leasta part of a boundary of the space between the final element of theprojection system and the substrate table. The liquid confinementstructure is substantially stationary relative to the projection systemin the XY plane though there may be some relative movement in the Zdirection (in the direction of the optical axis). In an embodiment, aseal is formed between the liquid confinement structure and the surfaceof the substrate. The seal may be a contactless seal such as a gas seal.Such a system is disclosed in United States patent applicationpublication US 2004-0207824 and European patent application publicationEP-A-1,420,298, each hereby incorporated in its entirety by reference,and illustrated in FIG. 5.

As shown in FIG. 5, a liquid supply system is used to supply liquid tothe space between the projection system and the substrate. The reservoir10 forms a contactless seal to the substrate around the image field ofthe projection system so that liquid is confined to fill a space betweenthe substrate surface and a final element of the projection system. Thereservoir is formed by a liquid confinement structure 12 positionedbelow and surrounding the final element of the projection system PL.Liquid is brought into the space below the projection system and withinthe liquid confinement structure 12. The liquid confinement structure 12extends a little above the final element of the projection system andthe liquid level rises above the final element so that a buffer ofliquid is provided. The liquid confinement structure 12 has an innerperiphery that at the upper end, in an embodiment, closely conforms tothe shape of the projection system or the final element thereof and may,e.g., be round. At the bottom, the inner periphery closely conforms tothe shape of the image field, e.g., rectangular though this need not bethe case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the liquid confinement structure 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air, synthetic air, N₂or an inert gas, provided under pressure via inlet 15 to the gap betweenliquid confinement structure 12 and substrate and extracted via outlet14. The overpressure on the gas inlet 15, vacuum level on the outlet 14and geometry of the gap are arranged so that there is a high-velocitygas flow inwards that confines the liquid.

There are several instances in an immersion lithographic apparatus wheredrying of a surface previously covered in immersion liquid is needed.For example, after imaging of a substrate, it is advantageous tocompletely dry the substrate. A gas knife can be used to dry previouslywet surfaces.

Several of the ways of containing immersion liquid in a lithographicprojection apparatus between the projection system PL and the substrateW are related to the so-called localized area solution in which asurface of the substrate which is, in plan, smaller than the totalsurface of the substrate is wetted with immersion liquid. A liquidconfinement system is used to contain the immersion liquid to only thelocalized area. A difficulty with an embodiment of such a localizedsolution is that during scanning of the substrate under the projectionsystem a seal is formed between the liquid confinement system and thesubstrate W which is contactless. One way of ensuring that immersionliquid does not escape from the liquid confinement system and therebycontaminate other parts of the apparatus is to provide a gas knifearound the periphery of the liquid confinement system to dry the surfaceof the substrate of any residual immersion liquid which has not beenremoved or contained by other components of the liquid confinementsystem. Indeed, a gas knife may be formed as part of a liquidconfinement system, such as in a liquid confinement structure whichsurrounds the space containing the immersion liquid and forms a seal tothe substrate.

In a liquid confinement structure 12 illustrated in FIG. 6, an extractor31 extracts liquid from the localized area to the left hand side of theFigure through gauze 30. The extractor 31 may extract both liquid andgas or only liquid. A recess 32 is provided radially outwardly of theextractor 31 and a gas knife 33 is provided radially outwardly of therecess 32. The gas knife forms a jet of gas 34 which is used to dry thesurface of the substrate W. In a similar embodiment illustrated in FIG.7, a modification of the recess 32 is made such that a passage 40 existswhich is open to a gas source, for example the atmosphere, such that aflow of gas from the passage 40 radially outwardly to a passage 50 whichis connected to a low pressure source is created. The gas knivesdisclosed can be used for general drying applications and in particularfor gas knives which may form part of a liquid confinement structure 12.

A gas knife typically works on the principle of inducing a shear forceon any residual liquid on a surface through a gas flow moving over thesurface of the residual liquid. This requires an extremely high flow ofgas out of the gas knife and also requires a narrow gap between thesubstrate W and the outlet of the gas knife (i.e. in the case of aliquid confinement structure 12, between the bottom surface of theliquid confinement structure 12 and the top surface of the substrate W).

By adjusting the configuration of the gas knife, a zone of increasedpressure can be created and a liquid can be prevented from passing thatzone. The zone is created by having a “curtain” of gas aimed at thesurface. This forms a high pressure liquid barrier and a pressuregradient can be formed in the liquid and it is the formation of thispressure gradient rather than the presence of a drag force at the liquidsurface which is effective to dry the surface by keeping the liquid toone side of the gas knife during movement of the substrate W or othersurface underneath the gas knife i.e. the pressure gradient is thedominant force. A pressure gradient can be formed at gas speeds ofbetween 50 m/s and 200 m/s. A controller is provided to regulate the gasflows and the height of the gas knife. A shear force mechanism can bearranged to remove the liquid.

By removing liquid by the formation of a pressure gradient, relativelylittle gas may be used compared to when the surface is dried by shearforces and a relatively large distance between the outlet of the gasknife and the surface being dried may be possible.

The gas knife will be described below in relation to drying of asubstrate W, in particular to the use of the gas knife in a liquidconfinement structure. However, the gas knife can be used for any otherapplication of drying a surface, perhaps for drying the top surface ofthe substrate table WT which may also have immersion liquid on it fromtime to time or any other component or indeed may be used for drying asubstrate or another component at a position in the immersionlithographic apparatus perhaps other than under the projection systemPL.

FIG. 8 illustrates schematically a gas knife generally labeled 33 and arecess or extractor generally labeled 32. The gas knife comprises anoutlet 310 in the form of a nozzle. Several variables are illustrated inFIG. 8. These are the width K of the nozzle outlet 310 of the gas knife(clearly the gas knife nozzle 310 is formed as a slit which has a lengthand a width, the slit extending into and out of the page in FIG. 8). Anangle A of the nozzle of the gas knife is illustrated which is the anglewhich the nozzle makes to a line perpendicular to the surface throughwhich the nozzle exits and perpendicular to the surface W to be dried.When the angle A is zero the gas knife nozzle is pointing directly down.Tb is the nozzle length and G is the distance between the nozzle outletand the surface W (in the embodiment where the gas knife is part of aliquid confinement structure, this is the so-called ‘ride height’ of theliquid confinement structure). A distance Li is the distance between thegas knife nozzle outlet 310 and the extractor 32, V is the velocity ofthe surface W relative to the gas knife 33, Qs is the gas flow throughthe gas knife 33, and Qe is the gas flow through the extractor 32.

As can be seen, the gas knife 33 comprises a chamber 320. Gas enters thechamber 320 and the size of the chamber relative to the outlet dampensany possible pressure fluctuations before the gas exits through nozzle310. A number of discrete inlets can be provided into the chamber 320for the introduction of gas into the chamber 320.

The extractor 32 has a chamber 410 similar to that of chamber 320 of thegas knife 33. The extractor 32 also has an inlet 420 which provides apassage between the bottom surface of the gas knife and the chamber 410.However the narrow passage with inlet 420 can be omitted so that thereis no narrowing between the chamber 410 and the inlet 420 in the bottomsurface; the gap G can provide enough resistance for flow equalization.

The forces which act on liquid on the surface W are drag forces whichoccur due to a shear force at the gas/liquid interface, pressure forceswhich are forces due to local pressure gradient, virtual mass or inertiaforces which are forces needed to accelerate a given volume of liquid,and general body forces. The last two components are related to movementof the surface whereas the first two components are determined by thegas knife design.

During optimization of the gas knife, the influence of evaporation ofliquid (e.g., water) should be accounted for. Evaporation depends on anumber of factors including temperature, humidity of gas, and gasvelocity (which depends on nozzle design). All may play an importantrole. Liquid evaporation is an undesirable phenomenon because it canlead to the cooling of the surface. Such cooling may deleteriouslyinfluence other things, most notably the substrate W surface shape, thetemperature of components in the apparatus, and/or the temperature ofthe immersion liquid (thereby changing the index of refraction of theimmersion liquid). Evaporation may be reduced or minimized by supplyinggas with a relative high humidity to the gas knife 33. The pressure dropover the length of the outlet or nozzle 310 of the gas knife 33 shouldalso be controlled to avoid cooling. In an embodiment using water andair, the pressure drop should not be greater than 0.2 bar otherwise thegas humidity will be decreased too much. Thus, the gas knife performanceshould be optimized for liquid removal as well as reducing or minimizingthe pressure drop in the nozzle 310.

A local pressure build-up between the surface to be dried, the gas knifeand the extractor of 0.05 bar gauge pressure or higher is sufficient fora flow regime of liquid being removed to be driven by a pressuregradient in the liquid rather than by shear forces. A local pressurebuild-up of 0.1 or even 0.2 bar gauge may be provided. If this can beachieved, in an embodiment using water, a residual liquid layerthickness of much less than 1 μm is possible (simulations and/orpractical tests have shown a residual water layer thickness of between200 and 400 nm is possible). There may be a negative relative pressureunder the exhaust area which exerts an attractive force on the surface Wtowards the gas knife 33. This will need to be compensated for in thecontrol dynamics of the apparatus if problems with imaging focus or ofcrashes is to be avoided and in any case the negative relative pressureshould be reduced or minimized.

The table below shows the effect of various parameters of the gas knifeon the relative pressure under the extractor (dP_(e)) and on thepressure drop over the nozzle length (dP_(n)).

Q_(s)/Q_(e) (l/min) T_(b) (μm) K (μm) G (μm) dP_(e) (Pa) dP_(n) (bar)100/110 500 35 200 ~−1300 0.22  100/110* 100 30 200 ~−2000 0.15 60/67500 10 200 1 140/155 100 55 200 0.05  90/100 500 35 150 ~−1700 0.18 82/90* 100 25 150 ~−2000 0.16 75/83 100 20 150 ~−2000 0.25

Escape of gas from the gas knife 33 out from under the assembly can bedeleterious to the performance of interferometers because theinterferometer beams may pass through gas that is badly conditioned. Oneway to substantially prevent this is to arrange for the exhaust flow Qeto be within about 20%, 10% or 5% of the gas knife flow Qs. Thevariables in the table marked with * are effective in this regard. Afurther advantage is that liquid can be collected from the other side ofthe gas knife 33 from the extractor 32 in this way. A disadvantage ofthis embodiment is that a deep under pressure is needed for this so thatforces exerted on the substrate W and substrate table WT are high andmay lead to deformations of the substrate W and any sensor on thesubstrate table WT.

A further exhaust 34 may be provided on the other side of the gas knife33 to the extractor 32. This is illustrated in dashed lines in FIG. 8.The design of the further exhaust 34 maybe the same as that of theextractor 32. This may reduce the relative under pressure in the exhaustregion and may therefore be desirable. The provision of two exhaustsdoes not lead to loss of performance. In this embodiment the gas flowmoves in two directions (radially inwardly and outwardly) from the gasknife. However, as it is the pressure gradient in the liquid and not thegas flow over the liquid which is applying the removing force to theliquid, the removal of liquid is substantially not deleteriouslyaffected.

The smaller the gap size G the more efficient extraction may be. This isbecause as the gap size G increases, a larger flow of gas and a thinnernozzle is needed to achieve the required pressure build-up but this isat the expense of an increased pressure drop over the nozzle length.However, decreasing the nozzle length leads to a narrowing of the nozzleand can lead to too high a negative pressure under the extractor. In anembodiment, the width of the nozzle may be 10 to 50 μm or between 25 and35 μm with a length Tb of between 100 and 500 μm. In order to have awell defined gas flow out of the nozzle, a ratio of nozzle length Tb tonozzle width K between 3 to 1 and 20 to 1 may be provided. If the gap Gis too large, the gas flow may diverge and the speed of the gas flow maybe too low. A gap size G of between 50 and 300 μm may be suitable. Anadvantage of a pressure gradient flow regime over a shear flow regime isthat height (i.e. gap size G) sensitivity is less.

The surface W should be moved in direction V illustrated in FIG. 8 suchthat a point on the substrate passes first under the extractor 32 beforepassing under the gas knife 33.

In order to reach a given gas speed (for example between 50 and 200 m/s)the flow rate out of the nozzle is proportional to the nozzle width Kand the length of the gas knife (in the direction perpendicular to theplane of FIGS. 6 and 7). The flow rate out of the gas knife shouldtypically be between 25 and 250 liters per minute. This means that thegas flow rate out of the gas knife should be between 75 and 750 litersper minute per meter length of the gas knife (with a nozzle width K ofbetween 10 and 50 μm).

In an embodiment, the gas knife may be between 0.2 and 8 mm or 1 and 8mm away from the extractor (distance Li). This range allows theestablishment of a pressure zone to block the passage of liquid as wellas shear action from gas passing over the surface of the liquid to movethe liquid towards the extractor. If the distance Li is too short, theshear force can be hard to generate and the liquid is not moved towardsthe extractor.

In an embodiment, it is advantageous to angle the nozzle away from thevertical position in either direction (i.e. to arrange for the angle Ato not be equal to zero). This helps in stabilizing the pressure zonewhich is formed by the gas knife 33. It is also possible to angle thegas exiting the nozzle 310 by balancing Qs and Qe accordingly and thisachieves the same advantages. If Qs and Qe are equal, or very similar,the flow of gas out of nozzle 310 does not deviate much from vertical.In an embodiment, a range of angle A is 5 to 20°. This means that it isarranged for gas to be blown onto the surface W at an angle of between70 and 85° to the surface. If the angle of the gas exiting the nozzle iscontrolled by varying Qe and Qs, Qe is between 0.4 to 0.45 Qs. The anglecan also be varied by changing the length Li of the lands between thenozzle and the inlet to the extractor 32 and the length Lo between thenozzle and the inlet to the further extractor 34 or the end of theassembly. Arranging for Li to be between 0.5 and 0.8 Lo should achievean exit angle of between 5 and 20° off vertical.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substratethrough a liquid, the apparatus comprising a gas knife configured toprovide gas to a surface to be dried at an angle to the surface ofbetween 70° and 85°.

In an embodiment, the lithographic projection apparatus furthercomprises an extractor positioned adjacent the gas knife to remove gas,liquid, or both, and a flow regulator configured to control a rate ofextraction of gas through the extractor and outlet of gas through thegas knife to achieve the angle. In an embodiment, an outlet of the gasknife and an inlet of the extractor are formed in a substantially flatsurface, the distance between the inlet of the extractor and the outletbeing 0.5 to 0.8 times the distance the flat surface extends on theother side to the extractor of the gas knife. In an embodiment, theoutlet forms an angle of between 85° and 70° with the surface.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substratethrough a liquid, the apparatus comprising a gas knife configured toprovide gas to a surface to be dried, a first extractor, and a secondextractor, the first and second extractors being on opposite sides ofthe gas knife and configured to remove gas, liquid, or both, from thesurface.

In an embodiment, a distance between the first extractor and the gasknife is 0.5 to 0.8 times the distance between the gas knife and thesecond extractor.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substratethrough a liquid, the apparatus comprising a gas knife configured toremove a liquid from a surface, the gas knife arranged such that passageof the liquid is blocked by a formation of a pressure gradient in theliquid.

In an embodiment, the apparatus further comprises a flow controllerconfigured to control flow rates of gas such that a local pressurebetween the surface, the gas knife and an extractor of at least 0.05 baris built up. In an embodiment, the gas knife is arranged to provide agas flow out of the gas knife at a speed of between 50 and 200 m/s. Inan embodiment, the gas knife is part of a dryer of the apparatus to dryitems after immersion in the liquid or part of a liquid confinementstructure which at least partly surrounds a space in which the liquid ispresent. In an embodiment, liquid is removed by shear action of gasflowing over the liquid.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substratethrough a liquid, the apparatus comprising a gas knife configured toprovide gas to a surface, wherein the gas knife comprises an outlet toexit gas, the outlet having a width of between 10 and 50 μm and a lengthof between 100 and 500 μm.

In an embodiment, the gas knife comprises a chamber positioned up streamof the outlet. In an embodiment, the outlet is in the form of a slit. Inan embodiment, the apparatus further comprises an extractor positionedadjacent the gas knife to remove gas, liquid, or both.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substratethrough a liquid, the apparatus comprising a gas knife configured toprovide gas onto a surface, an extractor adjacent the gas knife toremove gas, liquid, or both, and a flow regulator configured to controla gas flow rate out of the gas knife to be within 20% of a gas flow rateinto the extractor.

In an embodiment, the apparatus further comprises a positionerconfigured to control a position of the surface, when being dried, suchthat a point on the surface passes the extractor before the gas knife.In an embodiment, the gas flow rate out of the gas knife is between 75and 750 liters/minute/meter length of gas knife outlet. In anembodiment, an outlet of the gas knife is between 0.2 and 8 mm away froman inlet of the extractor.

In an embodiment, there is provided a device manufacturing methodcomprising projecting through a liquid a patterned beam of radiationonto a substrate, wherein liquid is removed from a surface by a flow ofgas out of an outlet of a gas knife which outlet has a width of between10 and 50 μm and a length of between 100 and 500 μm.

In an embodiment, there is provided a device manufacturing methodcomprising projecting through a liquid a patterned beam of radiationonto a substrate, wherein liquid is removed from a surface by a flow ofgas impinging on the surface at an angle of between 70° and 85°.

In an embodiment, there is provided a device manufacturing methodcomprising projecting through a liquid a patterned beam of radiationonto a substrate, wherein liquid is removed from a surface by formationof a pressure gradient in the liquid by gas.

In European patent application publication EP 1420300 and United Statespatent application publication US 2004-0136494, each hereby incorporatedin their entirety by reference, the idea of a twin or dual stageimmersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath or only on a localized surface area of the substrate. A liquidsupply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structuresthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise a combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets that provideliquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1.-19. (canceled)
 20. A lithographic projection apparatus arranged toproject a pattern from a patterning device onto a substrate through aliquid, the apparatus comprising: a liquid confinement structureconfigured to at least partly confine the liquid in a space between aprojection system and the substrate; a gas supply opening configured toprovide gas onto a surface; an extractor opening configured to removegas, liquid, or both; and a control system configured to arrange that agas flow rate out of the gas opening is within 20% of a gas flow rateinto the extractor opening.
 21. The apparatus of claim 20, wherein thegas supply opening and/or control system is configured to provide theflow of gas at an angle of between 5 and 20° off a perpendicular fromthe surface.
 22. The apparatus of claim 20, wherein the control systemis configured to cause a gas to flow out of the gas supply opening at aspeed of between 50 and 200 m/s.
 23. The apparatus of claim 20, whereinthe control system is configured to cause a gas flow rate out of the gassupply opening between 75 and 750 liters/minute/meter length of gassupply opening outlet.
 24. The apparatus of claim 20, wherein the gassupply opening is between 0.2 and 8 mm away from the extractor opening.25. The apparatus of claim 20, wherein the control system is furtherconfigured to arrange a local pressure build-up of 0.05 bar gauge ormore between the surface and the gas supply opening and/or extractoropening.
 26. The apparatus of claim 20, further comprising a positionerconfigured to control a position of the surface, when being dried, suchthat a point on the surface passes the extractor opening before the gassupply opening.
 27. A device manufacturing method comprising:projecting, using a projection system of a lithographic apparatus, apatterned beam of radiation through a liquid onto a substrate; at leastpartly confining the liquid in a space between the projection system andthe substrate; supplying a flow of gas through a gas supply opening ofthe lithographic apparatus onto a surface; extracting gas, liquid, orboth, through an outlet of the lithographic apparatus; and arrangingthat a gas flow rate out of the gas opening is within 20% of a gas flowrate into the extractor.
 28. The method of claim 27, comprisingsupplying the flow of gas at an angle of between 5 and 20° off aperpendicular from the surface.
 28. The method of claim 27, comprisingsupplying the flow of gas at a speed of between 50 and 200 m/s.
 30. Themethod of claim 27, further comprising arranging a local pressurebuild-up of 0.05 bar gauge or more between the surface and the gassupply opening and/or outlet.
 31. The method of claim 27, wherein thegas flow rate out of the gas opening is between 75 and 750liters/minute/meter length of gas opening outlet.
 32. The method ofclaim 27, wherein the gas supply opening is between 0.2 and 8 mm awayfrom the outlet.
 33. The method of claim 27, further comprisingcontrolling a position of the surface, when being dried, such that apoint on the surface passes the outlet before the gas supply opening.34. A lithographic projection apparatus arranged to project a patternfrom a patterning device onto a substrate through a liquid, theapparatus comprising: a liquid confinement structure configured to atleast partly confine the liquid in a space between a projection systemand the substrate; a gas supply opening configured to provide gas onto asurface; an extractor opening configured to remove gas, liquid, or both;and a control system configured to arrange a local pressure build-up of0.05 bar gauge or more between the surface and the gas supply openingand/or extractor opening.
 35. The apparatus of claim 34, wherein gassupply opening and/or the control system is configured to provide theflow of gas at an angle of between 5 and 20° off a perpendicular fromthe surface.
 36. The apparatus of claim 34, wherein the control systemis configured to cause a gas flow rate out of the gas supply openingbetween 75 and 750 liters/minute/meter length of gas supply openingoutlet.
 37. The apparatus of claim 34, wherein the gas supply opening isbetween 0.2 and 8 mm away from the extraction opening.
 38. The apparatusof claim 34, wherein the distance between the extractor opening and thegas supply opening is 0.5 to 0.8 times the distance a flat surfaceextends from the gas supply opening on the other side to the extractoropening.
 39. The apparatus of claim 34, further comprising a furtherextractor opening configured to remove gas, liquid, or both, from thesurface, the extractor opening and the further extraction opening beingrespectively on opposite sides of the gas supply opening.